CN117323851A

CN117323851A - Apparatus and method for preparing a slurry and coating a substrate with the slurry

Info

Publication number: CN117323851A
Application number: CN202310704228.8A
Authority: CN
Inventors: 金延宇; 鲍里斯·格拉格拉·莫雷诺
Original assignee: Initial Energy Ltd
Current assignee: Initial Energy Ltd
Priority date: 2018-04-26
Filing date: 2019-04-26
Publication date: 2024-01-02
Also published as: US11398628B2; EP3784376A2; US20210135227A1; CN113056324A; WO2020023095A3; US20190334176A1; CN113056324B; US20220320520A1; KR20210006918A; WO2020023095A2; JP2021526077A

Abstract

An apparatus and method for preparing a slurry for application to a substrate. The apparatus and methods of the present disclosure relate to providing slurry in an enclosed volume having at least one channel. The slurry comprises a solvent, a powder, and a binder. The slurry may also contain a dispersant. The slurry is repeatedly pushed through the at least one channel in a first flow direction and then returned through the at least one channel in a second flow direction opposite to the first flow direction under high pressure. The pushing uniformly disperses the powder and the binder in the solvent. Then, both sides of the substrate are simultaneously coated with the paste extruded from the closed volume after the pushing. Solidifying the coated slurry includes lyophilizing to preserve the porosity of the slurry on the substrate.

Description

Apparatus and method for preparing a slurry and coating a substrate with the slurry

Cross Reference to Related Applications

The present application claims priority from U.S. patent application Ser. No. 15/964,051, filed on 4/26 2018, which is hereby incorporated by reference in its entirety.

Technical Field

The present disclosure relates to an apparatus and method for preparing a slurry and coating the slurry onto a substrate.

Background

Forming a slurry containing the powder dispersed in a solvent and optionally a binder typically involves considerable energy and equipment. This is the case when forming a slurry for manufacturing a substrate for forming an electrode of a battery. For example, in a conventional wet electrode coating process, a viscous slurry containing a powder (like carbon black powder or other active/inactive materials) and an organic polymer as a binder is applied onto a substrate to form a current collector by pulling or delivering the slurry or substrate via various methods such as doctor blade, roll-to-roll (roll-to-roll) coater, etc. Conventional devices used in wet coating require a large amount of space because of the need to use doctor blades, roll-to-roll applicators, and the like. All the devices and workstations associated with conventional mixing, kneading, coating and drying are enormous.

A long period of time is also required to mix the slurry by using a conventional planetary mixer. Typically, a large amount of toxic solvents are also used in conventional wet-coated slurries to aid in forming the slurry and applying it to a substrate. For example, such toxic solvents include n-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, and the like. After the slurry is coated on the substrate, the toxic solvents must be removed. The removal requires well-designed evaporation techniques in the drying process to prevent environmental pollution and explosion. Drying requires a large dryer with a long belt conveyor combined with a heating system to evaporate the toxic solvents. In addition to the drying system, it is necessary to install a system for collecting the evaporated toxic solvent to prevent environmental pollution.

The dry coating process is an alternative to wet coating for manufacturing electrodes. However, dry coating has several drawbacks. For example, it is necessary to pulverize the dried carbon composite powder into a fine powder for coating, which requires two machines to pulverize the fine powder and distribute the fine powder onto the substrate. Specific hoppers and complex applicator arrangements are also required to disperse the fines onto the substrate.

Dry coating is also subject to inconsistent cell performance results based on the irregular distribution of fines on the substrate. The resulting non-uniformity of powder density on the substrate has a direct impact on many problems like adhesion and porosity uniformity between the coating and the substrate, which ultimately results in a lack of reaction uniformity. Even in the case of specially designed powder coating machines equipped with fine dispensers, there are the same kind of non-uniform cell performance problems.

Accordingly, there is a need for a coating apparatus and coating process that reduces the problems generally mentioned above in slurry formation and when applied to battery electrode manufacture.

Disclosure of Invention

One aspect of the present disclosure includes a process of coating a substrate with a slurry to form an electrode. The slurry comprises a powder. In some aspects, the powder may be formed from carbon black powder, or any conductive/nonconductive material or blend thereof. The slurry further comprises one or more solvents and a binder. The slurry may optionally contain one or more dispersants. The process further includes lyophilizing the coated substrate and heating the lyophilized coated substrate under vacuum at an elevated temperature to remove residual solvent. The process further includes calendaring the resulting coated substrate to be used as a battery electrode.

Another aspect of the present disclosure is an apparatus configured to mix and knead a slurry and then simultaneously apply the slurry to both sides of a substrate. The apparatus includes two cylinders connected via a narrow tube, each cylinder having a piston therein configured to repeatedly push (force) slurry back and forth between the cylinders and through the tube. The repeated movement of the slurry through the tube applies shear forces to the slurry, which mix and knead the slurry. In some aspects, an apparatus includes a die configured to extrude a slurry onto a substrate such that the slurry contacts both surfaces of the substrate simultaneously.

Further aspects of the disclosure include a method of coating a substrate comprising providing a slurry in an enclosed volume having at least one channel. The slurry includes a solvent, a powder, a binder, and a dispersant. The method further includes repeatedly pushing the slurry through the at least one channel in a first flow direction and then back through the at least one channel in a second flow direction opposite the first flow direction under high pressure to uniformly disperse the powder and binder in the solvent. The method further includes simultaneously coating both sides of the substrate with paste extruded from the enclosed volume after pushing.

Aspects of the disclosure also include: an electrode coated according to the above method; a battery having an electrode coated according to the above method; and a battery system having a plurality of battery cells, wherein each battery cell has an electrode coated according to the above method.

Further aspects of the disclosure include a method of curing a coated substrate comprising providing a substrate coated on both sides with a slurry. The slurry includes a solvent, a powder, a binder, and a dispersant. The method further includes freezing at least the solvent and the dispersant coated on the substrate and sublimating at least the frozen solvent and dispersant on the substrate. The method further includes heating the substrate under vacuum to above the freezing point of the at least one solvent and dispersant after sublimation and calendaring the substrate after heating.

Another aspect of the present disclosure includes a system having a first cylinder assembly with a first cylinder and a first piston. The first piston is configured to reciprocate within the first cylinder. The system also includes a second cylinder assembly having a second cylinder and a second piston. The second piston is configured to reciprocate within the second cylinder. The system also includes a channel connecting the first cylinder assembly to the second cylinder assembly. In operation of the system, the first cylinder assembly and the second cylinder assembly are configured to alternately apply compression and suction to the slurry within the first cylinder and the second cylinder to cause the slurry to reciprocate through the passage.

These and other functions of the disclosed devices, systems, and methods will be more fully understood upon review of the following drawings, detailed description, and claims.

Drawings

Fig. 1 illustrates a cross-sectional view of an apparatus for preparing a slurry in accordance with aspects of the present disclosure.

Fig. 2A illustrates a perspective view of a mold assembly according to aspects of the present disclosure.

Fig. 2B illustrates an exploded view of the mold assembly of fig. 2A with two mold parts in accordance with aspects of the present disclosure.

Fig. 2C illustrates a top view of the mold assembly of fig. 2A, in accordance with aspects of the present disclosure.

Fig. 2D illustrates a bottom view of the mold assembly of fig. 2A, in accordance with aspects of the present disclosure.

Fig. 3A illustrates a cross-sectional view of the apparatus of fig. 1 configured to apply a slurry to a substrate in accordance with aspects of the present disclosure.

Fig. 3B illustrates an optically transparent perspective view of the mold of fig. 3A applying a slurry to a substrate in accordance with aspects of the present disclosure.

Fig. 3C illustrates a cross-sectional view of the substrate of fig. 3B coated with a slurry along line 3B-3B in accordance with aspects of the present disclosure.

Fig. 4 is a flow chart of a process for coating a substrate according to aspects of the present disclosure.

Fig. 5 is a flow chart of a process for curing a coated substrate according to aspects of the present disclosure.

While the devices, systems, and methods discussed herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the description is not intended to be limited to the particular forms disclosed. Rather, the description is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.

Detailed Description

One or more embodiments of the devices, systems, and methods are shown in the drawings and will be described in detail herein with the understanding that the present disclosure is to be considered an exemplification of the principles disclosed herein and is not intended to limit the broad aspects to only the illustrated embodiments. For the purposes of this detailed description, the singular includes the plural and vice versa (unless specifically denied); the word "or" should be used both as conjunctions and as disjunctive conjunctions; the phrase "all" means "any and all"; the phrase "any" means "any and all"; and the phrase "comprising" means "including but not limited to". In addition, the singular terms "a/an" and "the" include plural referents unless the context clearly dictates otherwise. Each numerical range disclosed herein includes an upper numerical limit and a lower numerical limit, and each rational number (including each integer) therebetween.

Apparatus and processes for preparing a slurry and then applying the slurry to a substrate are disclosed. The apparatus and process of the present disclosure significantly reduces the complexity and time required to form and apply the slurry to the substrate. Also disclosed is a process for curing the slurry coated substrate. The disclosed apparatus and process may be used to manufacture electrodes for batteries. However, the apparatus and process may be used to form and apply any type of slurry to any type of substrate, and are not particularly limited to substrates intended for use with electrodes.

The apparatus and methods of the present disclosure reduce or eliminate the use of toxic chemicals as solvents and/or dispersants, such as NMP, DMF, acetone, etc., in the formation of electrode slurries when applied to the manufacture of electrodes of a battery. These apparatus and methods also shorten and simplify the overall process of battery electrode fabrication by removing complex conventional processes in preparing slurries, treating substrates, handling equipment, and the like. These devices and methods also reduce in size or eliminate the use of expensive and bulky devices for condensation, comminution and powder distribution for the processes discussed in the background above.

In particular, the method of the present disclosure uses only one device, which performs all of mixing, kneading, and coating. The device applies the slurry directly to the substrate in situ without the trouble of transferring the slurry from the mixing device to the application device, for example. The device also coats both sides of the substrate simultaneously. The method further includes lyophilizing the coated substrate, which removes the solvent. Lyophilization helps reduce damage or variation in the pore structure of the slurry and substrate formed during coating. The present disclosure also provides a slurry coating process in conjunction with a coating apparatus for manufacturing an electrode of an electrochemical cell. The electrochemical cell may be, for example, a primary or secondary cell, such as a lithium or fuel cell.

The slurry of the present disclosure is formed from a solvent, a powder, and a binder. The slurry may also contain a dispersant. In one or more embodiments, the solvent may be any chemical capable of dissolving the adhesive, and any chemical may be selected according to the desired adhesive characteristics. For example, the solvent may be water in the case of a water-soluble binder such as Polytetrafluoroethylene (PTFE). Alternatively, the solvent may be acetone (or nearly pure acetone), NMP or DMF in the case of a non-water soluble binder such as polyvinylidene fluoride (PVDF) powder or resin. In one or more alternative embodiments, the solvent may be any chemical capable of forming a dispersion with the binder and the powder.

The powder may be any powder used to make a dispersion. In one or more embodiments, the powder may be any powder used to fabricate an electrode. For example, the powder may be any electrochemically activatable, active, or inactive inorganic or organic material, or combination thereof. When the powder is a conductive powder, the conductive powder is used as an electrode or a conductive additive within an electrode of an electrochemical cell. The conductive powder may be carbon black powder, graphite, carbon fiber, etc., or a blend thereof. Other non-carbon powders may be, for example, silicon carbide (SiC), barium sulfate (BaSO) ₄ ) Lithium iron phosphate (LiFePO) ₄ ) Lithium iron manganese phosphate (LiMnFePO) ₄ ) And various oxides such as silicon dioxide (SiO ₂ ) Alumina (Al) ₂ O ₃ ) Lithium nickel cobalt aluminum oxide (linicomoo) ₂ ) Lithium nickel cobalt manganese oxide (LiNiCoMnO) ₂ ) Lithium manganese oxide (LiMn) ₂ O ₄ ) Lithium nickel manganese spinel (LiNi) _0.5 Mn _1.5 O ₄ ) Lithium cobalt oxide (LiCoO) ₂ ) Etc., as well as other natural minerals, and combinations thereof.

The non-carbon powders described above are all water soluble and hydrophilic. Thus, when using water-soluble and hydrophilic powders as described above, the ratio of water-based solvent to powder in the slurry can be further reduced to about 0.6:1 (by weight) due to the mixing and hydrophilicity of the materials as described below. This is in contrast to the ratio of hydrophilic powder to water-based solvent (which is about 1.25:1 by weight) in conventional wet processes. For carbon-based powders, the ratio of solvent to powder within the slurry may be about 4.5-8:1 by weight. This provides an advantage over conventional slurries that require a solvent to powder ratio of about 24-27:1 by weight. Thus, significantly less solvent must be used in the methods of the present disclosure, which reduces the amount of solvent that must be removed during curing.

The binder aids in adhering the powder to the substrate after application and curing. In one or more embodiments, the adhesive may be a resin adhesive. The binder may be soluble in the solvent, such as water-soluble, or may be in the form of a dispersion, such as a water-based polytetrafluoroethylene emulsion. Specific binders that may be used in battery fabrication include, for example, sodium carboxymethyl cellulose (Na-CMC), poly (sodium acrylate) (PAA-Na), poly (ethylene oxide) (PEO), poly (vinylpyrrolidone) (PVP), polyethylene glycol (PEG), poly (3, 4-ethylenedioxythiophene), water soluble acrylates (Acryl S020), polyvinyl alcohol (PVA), polyacrylamides and polymethacrylamides, divinyl ether-maleic anhydride, polyoxazoline, various types of polyphosphates used in tissue engineering, starch, liquid glucose, hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), carnauba wax, guar gum, xanthan Gum (XG), pectin, and the like, and combinations thereof.

In manufacturing an electrode, the amount of binder used in the slurry depends on how the binder affects the conductivity of the resulting electrode. In one or more embodiments, the binder to powder ratio within the slurry may be about 0.02:1 to about 0.1:1. However, a binder content of more than about 10wt% relative to the combined weight of binder and powder is not suitable for mass electrode production due to viscosity and energy-density considerations.

The dispersant helps mix the hydrophobic inorganic component (such as carbon powder) with the water-based solvent and binder. In one or more preferred embodiments, the dispersant is selected to be liquid and to have similar or inferior physical properties to the solvent, such as a lower melting/precipitation point. Similar or poor physical properties of the dispersant compared to the solvent lead to evaporation of the dispersant together with or before the solvent, such that the resulting film on the substrate after lyophilization contains mainly powder. For example, isopropanol having a precipitation point of-89 ℃ may be used, with water as solvent. Additional solvent residues (including non-aqueous solvents) may be extracted during lyophilization (such as in a lyophilizer condenser at-60 ℃ to-80 ℃) or subsequently during heating of the coated substrate at elevated temperatures, as discussed further below.

Dispersants that may be used in the slurry include, for example, isopropanol, ethanol, methanol, acetic acid, acetonitrile, acetone, NMP, DMF, and the like. Further, in one or more embodiments, some dispersants may also function as both dispersants and solvents. Further, while dispersants such as NMP and DMF are not preferred for use due to their toxic nature, they may still be used in the slurries of the present disclosure due to the much lower desired concentrations. For example, due to the benefits of the mixing and related devices discussed below, the amount of these dispersants can be much lower than conventional wet methods, which still reduces the costs associated with their use.

The amount of dispersant used in the slurry depends on other components within the slurry, including solvents. However, the slurry may be as low as 0.01 weight percent (wt%) dispersant. This is in contrast to conventional slurries that are mixed using conventional methods, which may require up to 30wt% dispersant in an aqueous solvent. For example, in the slurry of the present disclosure of carbon powder (water as solvent and PTFE emulsion as binder), the slurry is about 1wt% isopropyl alcohol when isopropyl alcohol is used as the dispersant. When NMP is used as the dispersant, the slurry may be as low as 0.01wt% NMP.

Referring to fig. 1, a cross-sectional view of an apparatus 100 for preparing a slurry 102 and coating the slurry 102 on a substrate is illustrated in accordance with aspects of the present disclosure. The device 100 includes a pair of cylinders 104a, 104b and a pair of pistons 106a, 106b. Each piston 106a, 106b is in one of the cylinders 104a, 104b (e.g., piston 106a is in cylinder 104a and piston 106b is in cylinder 104 b). The pistons 106a, 106b are connected to one or more devices (not shown) configured to drive the pistons 106a, 106b in a linear and reciprocating motion along the length (e.g., stroke length or direction) of the cylinders 104a, 104b, as indicated by line a. In one or more embodiments, the one or more means for driving the pistons 106a, 106b may be one or more linear actuators that may be controlled by a programmable driver. However, the one or more devices may be any type of mechanical and/or electromechanical device that may impart reciprocating linear movement to the pistons 106a, 106b. Synchronizing actuation of pistons 106a, 106b causes one piston to apply a compressive force to slurry 102 while the other piston applies a suction force.

The cylinders 104a, 104b are fluidly connected via a narrow tube 108. The narrow tube 108 allows the slurry 102 to flow between the cylinders 104a, 104b under the compressive force created by the actuation of the pistons 106a, 106b. By actuating pistons 106a, 106b to reciprocate within cylinders 104a, 104b, slurry 102 may repeatedly pass through tube 108. Thus, slurry 102 flows in a first flow direction from cylinder 104a through tube 108 and to cylinder 104b, such as in a left-to-right direction along line a in fig. 1. Slurry 102 then flows from cylinder 104b through tube 108 and to cylinder 104a, such as in a right-to-left direction along line a in fig. 1. The second flow direction is opposite to the first flow direction. Although the flow direction illustrated in fig. 1 is linear along line a, the flow direction may be non-linear in one or more embodiments. For example, the tube 108 may be U, S shaped, or have any number of identical and/or different bends that create a tortuous path for the slurry 102 to travel.

The repeated movement of slurry 102 through tube 108 mixes slurry 102. The narrow diameter of the tube 108 further facilitates mixing as compared to, for example, the diameter of the cylinders 104a, 104b in the stroke direction or flow direction (e.g., line a) of the pistons 106a, 106b. According to the bernoulli principle, the slurry 102 passing through the tube 108 experiences high shear forces resulting from velocity imbalance of particles within the slurry 102, which is based on particles at the edges of the tube 108 experiencing lower velocities than particles at the center of the tube 108. The shear forces applied when loading and/or discharging the slurry 102 into and/or out of the cylinders 104a, 104b result in high mixing efficiency and create a large kneading action.

The mixing efficiency depends on the flow rate of slurry 102 through tube 108, the diameter of tube 108, and the mixing time. The narrower the diameter of the tube 108 and the higher the flow rate of the slurry 102 through the tube 108, the more efficient the mixing and kneading. By way of example, a flow rate of 430 mm/s through a three-eighths inch inner diameter tube would take only 15 minutes of mixing. The 380 mm/s flow rate through a three-eighths inch inside diameter tube only takes 25 minutes of mixing. And a flow rate of 170 mm/s through an eighth inch inner diameter tube would take only 10 minutes of mixing. In practice, the diameter of the tube 108 may be about 1/16 to 1/2 inch. Thus, the configuration of the apparatus 100 provides for a higher mixing efficiency than conventional apparatus such as conventional planetary mixers. For example, mixing 30 grams of carbon black powder only consumes about 0.3 kilowatt-hours (kWh) of energy. For larger amounts of mixed materials, the power consumed may be up to about 10 to 15 kwh/kg of powder.

According to one example, the device 100 is formed from cylinders (i.e., cylinders 104a, 104 b) having a three inch inner diameter. The cylinders are connected by a tube (i.e., tube 108) that is 7 inches long and has an inside diameter of one eighth of an inch. The slurry (i.e., slurry 102) moved between the cylinders, pushing a 6 inch stroke through the pistons (i.e., pistons 106a, 106 b) at a piston speed of 1 millimeter/second. The slurry formed from the carbon black-polymer blend was thoroughly mixed and kneaded by the reciprocating movement of the piston and pushed through the tube and ready for coating in less than half an hour. However, the actual mixing and kneading time may vary depending on the size of the particles, the size (e.g., inner diameter, length) of the tube 108, and the speed of the pistons 106a, 106b, and thus the speed of the slurry 102 through the tube 108.

Although only one tube 108 is shown connecting the cylinders 104a, 104b, in one or more embodiments, there may be more than one tube 108 connecting the cylinders 104a, 104b. More than one tube 108 may be used when the diameter of the cylinders 104a, 104b in the stroke direction is large relative to the diameter of the tube 108.

The device 100 may be formed from one or more metals, metal alloys, or other materials (e.g., plastics). The materials used for apparatus 100 may depend on the solvent used to form the slurry. With water as the primary solvent for the slurry, the device 100 may be formed of a material that resists corrosion by water and other dispersants (such as 316 stainless steel).

In one or more embodiments, the apparatus 100 may include a third cylinder. The third cylinder may be attached to one of the cylinders 104a, 104b and/or the tube 108. The third cylinder may be used to accumulate the slurry prior to applying the slurry to the substrate, as discussed below. In one embodiment, the third cylinder may have any working volume that is greater than the working volume of cylinders 104a or 104b, such that the third cylinder may accumulate slurry 102 for subsequent coating after mixing, as described further below.

Referring to fig. 2A-2D, a mold 200 for applying slurry 102 to a substrate in accordance with aspects of the present disclosure is illustrated. As shown in fig. 2A and 2B, a mold 200 is formed from two mold parts 202A, 202B. The mold parts 202a, 202b may be symmetrical (as shown) or identical. Alternatively, the mold parts 202a, 202b may be asymmetric. Additionally, while the mold parts 202a, 202b are shown and described as each being a single part, in one or more embodiments the mold parts 202a, 202b may each be formed from multiple parts. The mold parts 202a, 202b are configured to apply a thin flat layer of slurry 102 simultaneously on both sides of the substrate, as described further below. The mold 200 includes an interface 204 (fig. 2A) configured to connect the mold 200 to one of the cylinders 104a, 104b or the tube 108 (or to a third cylinder, if present). The interface 204 includes two slurry inlet ports 206a, 206 b-one inlet port 206a, 206b for each mold part 202a, 202b, respectively. The inlet ports 206a, 206b are configured to receive slurry 102 extruded from the apparatus 100, which is extruded from one of the cylinders 104a, 104b or from the tube 108, depending on where the die 200 is attached.

Referring to fig. 2B, each mold part 202a, 202B further includes a slurry outlet port 208a, 208B. The outlet ports 208a, 208b are configured to uniformly apply the slurry 102 through the outlet ports 208a, 208b onto the substrate as the substrate passes through. The outlet ports 208a, 208b are approximately the same width as the substrate, but may be longer or shorter in width than the substrate.

The channels 210a, 210b connect the outlet ports 208a, 208b to the inlet ports 206a, 206b. The inlet ports 206a, 206b are configured to divide the slurry 102 into two separate streams. Thereafter, the channels 210a, 210b are configured to uniformly distribute the slurry 102 to the outlet ports 208a, 208b for subsequent distribution of the slurry onto the substrate.

Referring to fig. 2C and 2D, the mold parts 202a, 202b are coupled together to form the mold 200 and define a slit 212 through the mold 200. As described further below, the slots 212 allow the substrate to pass through the mold 200. Slurry 102 extruded from outlet ports 208a, 208b is applied simultaneously to both sides of the substrate passing through slit 212 as the substrate passes through die 200.

Referring to fig. 3A, a cross-sectional view of an apparatus 100 configured to apply a slurry 102 to a substrate 300 in accordance with aspects of the present disclosure is illustrated. The device 100 has been modified by disconnecting the tube 108 from the cylinder 104a. Instead of tube 108, die 200 is connected to cylinder 104a via interface 204. However, in one or more embodiments, the mold 200 may instead be connected to the tube 108 or cylinder 104b (or third cylinder). For example, the tube 108 may have an interface that connects to the interface 204 of the mold 200. The ability to reconfigure the apparatus 100 from the mixing, kneading configuration of fig. 1 to the application configuration of fig. 3A allows for simple and direct in situ coating without the need to transfer the slurry 102 from one apparatus (i.e., apparatus 100) to another.

As much slurry 102 as possible may be collected in cylinder 104a prior to attaching die 200. The slurry 102 within the cylinder 104a is then extruded from the cylinder 104a via actuation of the piston 106 a. The extruded slurry 102 enters the die 200 and is applied simultaneously to both sides of the substrate 300 from the outlet ports 208a, 208b. The substrate 300 may be any type of substrate, such as a substrate for forming an electrode. For example, the substrate may be foam, mesh, or any type of porous, semi-porous, or non-porous material.

Fig. 3B illustrates the slurry 102 entering the inlet ports 206a, 206B, being directed into the channels 210a, 210B, exiting the die 200 through the outlet ports 208a, 208B, and then onto the substrate 300. The pressure of the slurry 102 exiting the outlet ports 208a, 208b pushes the slurry 102 into the substrate 300, such as into the pores of the substrate 300.

In one or more embodiments, the application of slurry 102 to substrate 300 also results in substrate 300 advancing through die 200 via slit 212. In other words, applying slurry 102 to substrate 300 may move substrate 300 in a desired direction, such as downward in the orientation of fig. 3B. Alternatively, or in addition, an additional driving force such as a winding device (not shown) may be used to drive the substrate 300 through the mold 200.

Fig. 3C illustrates the applied slurry 102 on a substrate 300. In particular, the slurry 102 forms thin films 302a, 302b on both sides of the substrate 300. These films may be about 8 μm to about 25 μm (micrometers) thick. Applying the films 302a, 302b according to the disclosed process results in a uniform thickness on both sides of the substrate 300. In addition, the thickness may be controlled by the speed of the piston 106a in combination with the speed of the substrate 300 through the slit 212 in the die 200 during extrusion of the slurry 102 from the cylinder 104a.

In one or more embodiments, after mixing the slurry 102 but before applying the slurry 102 to the substrate 300, the slurry 102 may be exposed to a vacuum within one or both cylinders 104a, 104b (or a third cylinder). The vacuum assists in removing gas from the slurry 102 prior to coating. The gas within the slurry 102 may affect the surface uniformity and adhesion of the thin films 302a, 302b of the slurry 102 produced on the substrate 300. Thus, removal of the gas improves the uniformity and adhesion of the slurry 102.

Fig. 4 is a flow chart of a process 400 for coating a substrate in accordance with aspects of the present disclosure. The process 400 is performed using the apparatus 100 disclosed above. Process 400 begins in step 402 with slurry in apparatus 100. The device 100 as disclosed above has an enclosed volume (with at least one channel) defined by the cylinders 104a, 104b and the tube 108. The slurry may be any of the slurries disclosed herein and may contain solvents, powders, binders, and dispersants. In one or more embodiments, the slurry may lack a dispersant. As disclosed above, the binder in the slurry cannot exceed 10wt% relative to the combined weight of binder and powder. The ratio of water-based solvent to powder in the slurry may be about 4.5-8:1 by weight. The amount of dispersant in the slurry can be as low as 0.01wt%. However, the amount of dispersant in the slurry, if any, is typically about 1 to 2wt%. As an example, the slurry may be formed from water as a solvent, carbon black as a powder, polytetrafluoroethylene emulsion as a binder, and alcohol as a dispersant, although any of the components disclosed above may be used. Importantly, the slurry does not require n-methyl-2-pyrrolidone or additional toxic dispersant based on the ability of the apparatus 100 to produce a dispersion from the slurry without the toxic dispersant.

At step 404, the slurry is repeatedly pushed through the at least one channel in a first flow direction and then returned through the at least one channel in a second flow direction opposite the first flow direction under high pressure to uniformly disperse the powder and binder in the solvent. As disclosed above, each of the two cylinders includes a piston, and the reciprocating actuation of the two pistons pushes the slurry to flow in a first flow direction and a second flow direction. The cylinder is configured such that the cross section of at least one channel is smaller than the cross section of the cylinder in the stroke direction of the two pistons. This results in high shear forces on the slurry as it passes through the tube, which results in mixing of the slurry. For example, the inner diameter of each channel may be about 1/16 inch to 1/2 inch, and the inner diameter of the cylinder may be much larger, such as about 3 inches or more. In one or more embodiments, the inner diameter may be less than 3 inches depending on the velocity of the piston within the cylinder.

In step 406, both sides of the substrate are coated simultaneously with the paste extruded from the enclosed volume. The coating may be a thin film of the slurry at a desired thickness, as discussed above. In one or more embodiments, a vacuum may be applied to the slurry within the apparatus 100 prior to step 406 but after step 404 to remove gases that may have formed within the slurry during previous process steps.

The solvent and dispersant used to form the slurry allow for a process of curing the slurry on the substrate that is different from conventional processes. In particular, since a small portion of the volatile organic solvent (such as the alcohols described above) is used to disperse the hydrophobic material (like carbon powder) in the water-dominant solution, a lyophilization process can be used to remove the solvent and dispersant and dry the coating. The lyophilization process reduces the likelihood of problems found in conventional electrode manufacturing processes. These problems include uncontrolled deformation of the pore structure upon drying and defects in the morphology and porosity of the film.

Fig. 5 is a flow chart of a process 500 for curing a coated substrate (as a final product) in accordance with aspects of the present disclosure. Process 500 begins at step 502 with a substrate coated with a slurry on both sides. The substrate may be coated according to the process 400 disclosed above, and the slurry may be any slurry based on aspects of the present disclosure.

At step 504, the solvent and dispersant coated on the substrate are frozen. Freezing can occur according to any process that reduces the temperature of the solvent and dispersant below their freezing point. However, in one or more embodiments, when the amount of dispersant used is negligible relative to the amount of solvent, it is not necessary to freeze the dispersant, such as in the case of 1wt% isopropyl alcohol in the present invention.

At step 506, after freezing the solvent and dispersant, the solvent and dispersant within the coated substrate are sublimated to freeze-dry the substrate. Sublimation can occur according to any process that results in sublimation of the solvent and dispersant.

At step 508, after sublimating the solvent and dispersant, the substrate is heated in vacuo to above the standard freeze point of the solvent and dispersant. The heat and vacuum treatment further aids in removing any remaining solvent and dispersant from the substrate.

At step 510, after heating, the substrate is calendered. In one or more embodiments, calendering includes cold calendering the substrate to stabilize the coating on the substrate. In one or more embodiments, calendering further comprises hot rolling the substrate after cold calendering. The hot rolling may be from about 100 ℃ to about 150 ℃ to improve the adhesion of the film to the substrate. In addition to improving adhesion, hot rolling also improves electrical conductivity through improved adhesion.

Although porosity within the film may be lost during calendaring, the characteristics of the pore structure of the film after lyophilization remain superior to the pores of any coating made by conventional methods in battery electrode fabrication in terms of uniformity and homogeneity. Thus, the coating process produces a uniform coating on the substrate that has a porosity that is superior to that heretofore obtained by conventional processes. The coating is relatively defect free compared to conventional methods, creating very low rates of pinholes, bubbles, pits (divots), streaks, foreign contaminants, overly inhomogeneous coating regions or agglomerates on the surface of the coating.

Thus, the methods and apparatus of the present disclosure reduce the use or amount of toxic materials in forming the slurry, or completely remove toxic materials, such as toxic solvents that cause undesirable vapors during the production of battery electrodes. Reducing or removing toxic materials reduces or eliminates the specialized equipment required to prevent the release of toxic materials into the environment and other problems such as explosions. The methods and apparatus of the present disclosure also reduce the required working space required for electrode fabrication compared to conventional processes.

The present disclosure may include the following embodiments.

Embodiment 1. A method of coating a substrate, the method comprising the steps of: providing a slurry in an enclosed volume having at least one channel, the slurry comprising a solvent, a powder, a binder, and a dispersant; repeatedly pushing the slurry through the at least one passage in a first flow direction and then back through the at least one passage in a second flow direction opposite the first flow direction under high pressure to uniformly disperse the powder and the binder in the solvent; and simultaneously coating both sides of the substrate with the slurry extruded from the enclosed volume after the pushing.

Embodiment 2. The method of embodiment 1, wherein the ratio of the binder to the powder is about 0.02:1 to about 0.1:1 by weight.

Embodiment 3. The method of embodiment 1, wherein the ratio of solvent to non-carbon powder is about 0.6:1 to about 1.25:1 by weight.

Embodiment 4. The method of embodiment 1, wherein the slurry is about 0.01 to 2wt% of the dispersant.

Embodiment 5. The method of embodiment 1, wherein the ratio of solvent to carbon powder is about 4.5:1 to about 8:1 by weight.

Embodiment 6. The method of embodiment 1, wherein the enclosed volume comprises two cylinders connected by the at least one channel, and wherein each of the two cylinders comprises a piston, and reciprocating actuation of the two pistons pushes the slurry to flow in the first flow direction and the second flow direction.

Embodiment 7. The method of embodiment 6, wherein a cross section of each of the at least one channel in the first flow direction is smaller than a cross section of the cylinders in a stroke direction of the two pistons.

Embodiment 8. The method of embodiment 7, wherein each of the at least one channel has a diameter of 1/16 inch to 1/2 inch.

Embodiment 9. The method of embodiment 1, wherein forming the powder and the dispersion of the binder in the slurry requires about 10 to 15kWh of energy per kilogram of solid powder.

Embodiment 10. The method of embodiment 1, wherein the slurry lacks n-methyl-2-pyrrolidone.

Embodiment 11. The method of embodiment 1, wherein the solvent is water.

Embodiment 12. The method of embodiment 11, wherein the powder is carbon black powder.

Embodiment 13. The method of embodiment 12, wherein the binder is polytetrafluoroethylene emulsion.

Embodiment 14. The method of embodiment 13, wherein the dispersant is an alcohol.

Embodiment 15. The method of embodiment 1, further comprising applying a vacuum to the enclosed volume to remove gas from the slurry prior to the coating.

Embodiment 16. An electrode coated according to the method of embodiment 1.

Embodiment 17. A battery having an electrode coated according to the method of embodiment 1.

Embodiment 18. A battery system having a plurality of battery cells, each of the battery cells having an electrode coated according to the method described in embodiment 1.

Embodiment 19. A method of curing a coated substrate, the method comprising the steps of: providing a substrate coated on both sides with a slurry comprising a solvent, a powder, a binder and a dispersant; at least freeze-coating the solvent and the dispersant on the substrate; sublimating at least the solvent and the dispersant frozen on the substrate; heating the substrate under vacuum after the sublimation to above the standard freezing point of the at least one solvent and the dispersant; and calendering the substrate after the heating.

Embodiment 20. The method of embodiment 19, wherein the calendering comprises cold calendering the substrate to stabilize the coating on the substrate, followed by hot rolling the substrate.

Embodiment 21. The method of embodiment 19, wherein the solvent is water.

Embodiment 22. The method of embodiment 19, wherein the powder is carbon black powder and the substrate forms an electrode of a battery cell.

Embodiment 23. The method of embodiment 19, wherein the binder is polytetrafluoroethylene emulsion.

Embodiment 24. The method of embodiment 19, wherein the dispersant is an alcohol.

Embodiment 25. The method of embodiment 19, wherein the slurry lacks n-methyl-2-pyrrolidone.

Embodiment 26. A system, the system comprising: a first cylinder assembly having a first cylinder and a first piston configured to reciprocate within the first cylinder; a second cylinder assembly having a second cylinder and a second piston configured to reciprocate within the second cylinder; and a channel connecting the first cylinder assembly to the second cylinder assembly, wherein, in operation, the first cylinder assembly and the second cylinder assembly are configured to alternately apply compression and suction to the slurry within the first cylinder and the second cylinder to reciprocate the slurry through the channel.

Embodiment 27. The system of embodiment 26, further comprising: a die assembly connected to the first cylinder assembly and having two sub-die parts, wherein each sub-die part has an inlet channel for receiving slurry from the first cylinder assembly and an outlet configured to extrude the slurry onto a substrate passing through the die assembly.

Embodiment 28. The system of embodiment 26 wherein the two sub-mold parts assembled form a channel for a substrate to pass through for extruding the slurry onto both sides of the substrate simultaneously.

While the present disclosure is directed to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the present invention. It is also contemplated that additional embodiments according to aspects of the invention may combine any number of features from any of the embodiments described herein.

Claims

1. A method of coating a substrate, the method comprising the steps of:

providing a slurry in an enclosed volume having at least one channel, the slurry comprising a solvent, a powder, a binder, and a dispersant;

repeatedly pushing the slurry through the at least one passage in a first flow direction and then back through the at least one passage in a second flow direction opposite the first flow direction under high pressure to uniformly disperse the powder and the binder in the solvent; and

both sides of the substrate are simultaneously coated with the slurry extruded from the enclosed volume after the pushing.

2. An electrode coated according to the method of claim 1.

3. A battery having an electrode coated according to the method of claim 1.

4. A battery system having a plurality of battery cells, each of the battery cells having an electrode coated according to the method of claim 1.

5. A method of curing a coated substrate, the method comprising the steps of:

providing a substrate coated on both sides with a slurry comprising a solvent, a powder, a binder and a dispersant;

at least freeze-coating the solvent and the dispersant on the substrate;

sublimating at least the solvent and the dispersant frozen on the substrate;

heating the substrate under vacuum after the sublimation to above the standard freezing point of the at least one solvent and the dispersant; and

the substrate is calendered after the heating.

6. A system, the system comprising:

a first cylinder assembly having a first cylinder and a first piston configured to reciprocate within the first cylinder;

a second cylinder assembly having a second cylinder and a second piston configured to reciprocate within the second cylinder; and

a passage connecting the first cylinder assembly to the second cylinder assembly,

wherein, in operation, the first cylinder assembly and the second cylinder assembly are configured to alternately apply compression and suction to the slurry within the first cylinder and the second cylinder to reciprocate the slurry through the passage.